ABSTRACT The shift from high school to college coincides with a dramatic increase in substance use and new peer social influences. Despite the robust literature supporting the importance of peer dynamics for alcohol use, alcohol interventions have not incorporated elements that utilize peer influence for reducing hazardous alcohol use. An approach that takes the campus social ecology into consideration and that specifically leverages peer influences within college social networks may be more impactful and sustainable than currently established college alcohol intervention approaches. This treatment development research will follow the stage model of behavioral therapies research to create an innovative intervention in which college students in first-year dormitories are identified and engaged to assist in reducing the alcohol-related risk behaviors of their peers. Initial intervention development will entail conducting focus groups (4-5 groups, N = 32) to produce the intervention components using elements from Bystander Intervention and Brief Motivational Intervention approaches. An open trial phase will use social network analysis methods to collect information about friendship ties within one first-year college dormitory network and will randomly select participants to receive the new intervention (final N = 15 intervention recipients). The general goals for the intervention recipients are to increase concern and awareness about hazardous alcohol behavior in the community, assume responsibility for community safety, and develop the skills and self-efficacy to intervene with peers. Following the open trial, we will refine the intervention and counselor training procedures, then will conduct a small randomized controlled trial using two size-matched first-year dormitories (N = 30 intervention recipients; N = 260 networked peers) comparing the new intervention (Bystander Brief Motivational Intervention) in one dormitory to a natural history control in the other. The goal of the RCT is to demonstrate feasibility, acceptability, adequacy of counselor performance, and preliminary efficacy of the intervention. Intervention outcomes will be measured on the intervention recipients and their networked peers. We expect participants who live in the dormitory assigned to the new intervention will show evidence of greater reduction in number of heavy drinking days and negative consequences at 1 and 3 months relative to the control. We also expect that theoretically supported cognitive and behavioral processes targeted in the new intervention will be associated with reductions in the target behaviors. Our final goal will be to establish whether intervention recipients with high centrality (determined through network ties) are more effective alcohol harm reduction bystanders. This research has the potential to produce an efficacious brief intervention that can reduce hazardous drinking in the larger community via network diffusion. Findings have the potential to advance alcohol use prevention among various intact networked ecologies.